Funding is requested to purchase a state-of-the-art Siemens Inveon dedicated positron emission tomography (DPET) for our continuing in vivo small laboratory animal research efforts at Stanford. The system will be installed in the Stanford Center for Innovations in In Vivo Imaging (SCi3), a service center that provides the infrastructure and expertise to conduct in vivo small animal imaging studies. The SCi3 small animal imaging resource supports many individual as well as multi-investigator program research projects. High resolution PET systems capable of studying disease in small laboratory animal models are playing an important and fundamental role to image suitable animal models of disease in order to guide the development of new molecular probes and assays that study the basic molecular processes associated with disease states in their natural environment within a living subject, and help to discover and monitor the efficacy of new molecular- based treatments. The existing Concorde/Siemens microPET R4 currently installed at the SCi3 service center has been extensively used for mouse, rat and primate imaging studies. However, the microPET R4 scanner, a 10 year-old, first generation small animal PET-only system with dated performance and declining health, has outlasted its projected use and both parts and service are no longer available for it. Breakage of the microPET R4 scanner would terminate all ongoing NIH-funded rat and small primate studies. Thus, the proposed Siemens Inveon DPET system was chosen to replace the existing and obsolete microPET R4. The Inveon DPET system will substantially advance our PET performance capabilities, including improving the volumetric resolution by over factor of four, as well as enabling us to study larger rodents (e.g., rats, rabbits) and small primates (e.g., squirrel monkeys), animals that cannot be imaged using the Siemens Inveon multimodality PET-CT scanner that is also installed in the SCi3 service center. The proposed system will be placed in the SCi3 service center and used to support current and future NIH-funded research ranging from studying the molecular basis of cancer, cardiovascular and neurological diseases to developing cellular-based therapies. It will also be used to evaluate the pharmacokinetics and efficacy of a range of new diagnostic and therapeutic agents under development by Stanford faculty. Relevance to human health: Prior to applying novel diagnostic and therapeutic compounds for clinical use, preclinical studies are required to validate new probes in appropriate models in mice, rats and primates, as well as larger animals. The proposed system will provide superior molecular sensitivity, resolution, field-of-view, and reliability for Stanford NIH-funded researchers to study and develop the next generation of molecular probes and assays designed for studying the molecular bases of disease, and guiding the discovery and monitoring of novel molecular-based treatment. The successful probes, assays, and treatments enabled by the proposed Inveon system will be validated for safety and efficacy and then directly translated to the clinic to improve the management of human diseases.